Data writing of memristors with light would help to overcome some important issues related to data-transfer, therefore further reducing the power consumption, and to integrate memory and optical sensing functionalities attractive in robotics. Ferroelectric materials show multistate spontaneous switchable polarization that can be sensed by two terminal resistance probing, so these can act as memristors.

In addition, ferroelectrics are optically active materials. Therefore, ferroelectrics are ideal candidates to be studied as optoelectronic memristors. However, the light control of polarization direction (up or down) is challenging.

"In our work, published in Materials Horizons, we show that internal electric field engineering combined with optical stimuli can be used to control ferroelectric polarization state. More precisely, it is shown that appropriate ferroelectric/metal structures allow to select the direction of imprint electric field. This ability is further exploited by demonstrating the optical control of the resistance states in a ferroelectric capacitor" explains Ignasi Fina, ICMAB researcher. 

New concepts

Ferroelectric materials are fascinating and useful because they show spontaneous electric polarization and it is strongly coupled to long-range electric and stress fields. Piezoelectricity and electrically switchable polarization arise from these coupled magnitudes. Alternatively, optical control of ferroelectric polarization is of interest for new envisaged devices integrating optical sensing, logic and memory functionalities. The fact is that light is coupled to ferroelectric polarization.

However, light cannot univocally determine the final polarization sign and therefore subsidiary tools are needed to unbalance one of the degenerated polarization states. In this communication, the authors evidence that light can selectively produce up-to-down or down-to-up polarization switching by manipulation of the internal electric field's sign and magnitude. Remarkably, the final polarization state remains after optical stimuli. This method consists in the unbalancing of the internal electric fields, and therefore ferroelectric polarization final state, by appropriate electrode selection.

The significance of the developed method combining a photoelectric response and manipulation of internal electric fields has been proven useful in devices with capacitator structures, where resistance can be also selectively switched high-to-low or low-to-high by light. 

Abstract